Frequency-responsive network



Jan. 1'4, 19141. R, FR'EEMAN Re.2l,691

` FREQUENCY-RESPONSIVE NETWORK original Filedsept. 2o. 19:58

BERT L. FR MAN BY A ATTORNEY Reuma Jan. 14, 1941 rnEoUENcLaEsPoNsrvE Narwoax neben r.. Freeman, nachm, N. y., mmm to Haaeltine Corporation,

a corporation of Dela- Orlglnal No. 2,184,072. dated December 19, 1939, l

Serial N0. 230,820, September 20, 1938.

Application for reissue June 2,1, 1940, Serial No.

- y1': claims. (cuss-4o) The present inventiton relates to an improved frequency-responsive network and particularly to such a network adapted. to be utilized in an 'automatic-frequency control system of a modulated-carrier signal-translating apparatus, the frequency-responsive network 'of the invention having a relatively limited response range'but y having a relatively high sensitivity over the range. As used in this specification, the terms relatively limited response range" and "limited frequency range refer to a range of frequencies which is narrow relative to the mean frequency of the range.

One type of frequency-selective network which has previously been used in automatic-frequency control systems utilizes the principle of rectifying separately the sum and the dierence of the voltages existing across the primary and secondary windings of a double-tuned circuit and differentially combining the rectified voltages so obtained to provide a voltage varying in magnitude and polarity with deviations of the frequency of the signal input to the system from its mean or normal value. A disadvantage of such an, arrangement is that with usual design of sig-naltranslating and control circuits and at usual signal frequencies, the magnitude of the output of each of the rectiilers varies quite gradually' t vide a frequency-selective network operable over a relatively narrow frequency range at'the frequencies commonly utilized in the intermediatefrequency channel ofsuperheterodyne' receivers.

It is still another object of the invention to provide a frequency-responsive network operable over a relativelyl narrow frequency range and having a relatively high sensitivity over the range. v l l In accordance with the invention. a frequency-responsive network for operation over a given frequency range comprises means for developing from an applied .signal a first voltage whichvdecreases with frequency in the vicinity of the mean frequency of the range and means for developing from the applied signal a second voltage which increaseswith frequency in the vicinity of the mean frequency'oi' the range. network includes means for applying each of the two voltages to one of a pair of rectifiers. There is also provided means for applying a parttof the output voltage ol each rectifier as a delay bias on. the other rectifier. each of the bias voltages being sufficient to reduce the output of the rectiiler to which itis applied tozero at a frequency in the vicinity of the mean frequency of the range. The network further in- Thecludes means for deriving from the output of each of the rectiflers an effect which varies in accordance -with the frequencyof the applied signal. As used in this speciilcation. the term delay bias is intended to mean an amplitude delay bias. y In accordance with one embodiment of the invention, a frequency-responsive network comprises an vinput circuit to which is coupled means for deriving a tlrst voltage and means for deriving a second voltage variable in'phase with frequency over the operating range of the system with respect to the nrst voltage. Two rectiers are provided together with means for applying to one of the rectifiers the sum and to the other of the rectiilers the difference of the two derived voltages, and means for applying an amplitude delay bias to each of the rectiflers derived from the applied voltages. `Each of the biases is sumf cient to reduce the 'output' of the rectiner to which it is applied to substantially zero at a frequency in the immediate vicinity of the mean resonant frequency of the operating range.

Means are provided for deriving an output from the system which varies in accordance with the voltages developed by the rectifiers.y

' In a preferred embodiment of the invention.

the means of obtaining the two derived voltages. the relative phase of which varies, comprises inductively-coupled tuned circuits. one of the voltagesbeingthatacrosstheprimarytunedcircuit and the Aother being ,that across the secondary tuned circuit'Also inaccordancewithapreferred'embodiment of the invention. the abovementioned rectifiers are of the diode type and .have individual load circuits including a common load impedance and' individual load impedances. the value of the individual impedance! being smaller than that ff the common impedance. In this embodiment. the common impedance comprises the means for developing the delay biases, a biasbeing developed thereacross swplyllandappliedoverconductorilto other rectifier.

, In snotherembodiment of the invention the rectifiersareofthetriodetypeandthemutual delay biases are developed by self-rectification in the grid circuits of the rectiilers. V

The novel features which are believed to characteristic of this invention are set forth with particularity in the appended claims. The in'- vention itself,.however. both as to its organization and method of operation. together with further objects thereof. will best be understood by reference to the speciiicatlon taken in connection with the accompanying drawing in which Fig. l is a circuit diagram, partly schematic. of a complete superheterodyne receiver including an automatic-frequency control system embodying the present invention: Pigs. 2 ands illustrate certain of the operating characteristics of the circuit of F18. 1: and 171g. 4 illustrates aimerait embodiment of a frequency-responsive network constructed in accordance with the invention.

Refeningtong.iofthedrawlng.thereis shown a circuit diagram. partially schematic. of a complete modulated-carrier signal receiver of the superheterodyne type embodying the linvention. i'hisv receiverv comprises. in cascade. an antenna-ground circuit.- Il. il. a radio-frequency ampliner l2. a frequency changer or oscillator-I modulator Il. intermediate-frequency ampliiiers il and Il, another vstage of intermediate-frequency ampliilcationcomprising a vacuum tube I I and a frequency-responsive selector network l1, a detector and automatic control or A. V. C. supply il. an audio-frequency amplifier of one or more stages Il.' and a sound reproducer 2l. Automatic amplification control lssecm'edinawell-knownmannerbyaunidirectional bias voltage derived from theA. V.

controlelectrodesofoneormoreof structicna'ndarrangement.

Negiectingforthemomenttheoperationof thatpar'tofthesystemembodyhgtheprsent being Inbrietsignalslntereeptedbyantmna-grmd eircuitll.iiareseleetedandamplifiedinradio amplifierilandtranshtedtooseilla- MW! tmfdnluiulatorilwhereiutlicyai'eeollvertedto an intermediate-beaune! mediate-frequency signal is in intermediate-frequency signal. v'l'lie interforreproduetion. automatic-mation eontroiiiiasdelivedtromunitiiiseileetlveto 2 21,601 by-eachoftherectiiiercircuitsandappliedto the amplidusll. IlaudA controltheamplincationofoneormoreoithe units i2. I8. Il and iltomaintain thellgnalinput'to the detector il within a relatively narrow range for a wide range of received signal intensitios. while the automatic-frequency control bias derlvedfrom unit I1 is effective to control theA` frequency-adjusting device 2l to maintain the frequency ot the signal input to the detector Il at a substantially constant value. o

`Referring now more particularly to the circuit of the invention for'deriving a potential automatically to control the tuning of the receiver.

of the voltage across the primary tunedcircuit 33, Il and the voltage across half lthe secondary tuned circuit $2, $3. Rectiilers N and 3l comv prise individual load circuits having .a common impedance,`shown as a .resistor 3B. and individual impedances, shown respectively as resistors 31 and IB. To this end, resistor is connected between the common terminal of resistors I1 and 8l and a mid-tap on inductance I2, while a coupling condenser Ii-is connected between the high potential side of tuned circuit SII, ll and the mid-tap on inductance il. A by-pass condenser Il is connected across load resistors 31 and Il in l series. As explained further hereinafter, the value of resistor l. should be at least of the same order` of magnitude as, preferably severaltimes greater than, that of resistors I1 and Il.

In considering the operation of the circuit Just described. it will be seen that. neglecting resistor ll, the frequencyselective network l1 is in .general similar to conventional'frequency-reaponsive networks utilising the principle of rectifying separately the sum and difference of the voltages across primary and the secondary of a doubletuned circuit and combining differentially the f rectiiled voltages` so obtained to provide a voltage 'varying in magnitude and polarity with the ix'e'-l quency applied to the system. Fora complete explanation of the elect of resistor on the characteristics of the frequency-responsive network i1. reference ispme to Pig. 2 in which-the curves represent the unidirectional output current of one of the rectiiiers'. for example diode Il.

as a function of frequency. for various values of corresponding relator. lThe' characteristics ofdiode8larenotsliownbutaresimilartothose `ofdiode84butxotatedi80degreesaboutthever ticallaxisoftheiigure. ThecurveforRas=0ls representative of the conventional discriminator circuitsoftheprlorart,mentionedabove.in wiuchtheresistanceofthecommonportionof the tworeetifier circuits is either 'aero' or some valueverysmallrelativetothatofreaistorsil andll. Theothercurvesformccessivelyim" creasinsvaluesoi'resistorltindicatethatdiode.

iseutoiiat valueotlsnisincre'ased. l'lhcutoifisduetothefacttliattheliiasdevelopedacroesresistorllbythecurrentofdiode il exceeds e peaks of the intermediate-frm. Wwltaseappliedtodiodeuwmscdiode aussi diode Il is biased to cutoff by the delay bias across resistor I4 'developed by diode I4. In the frequency range between the point of maximum response of diode I4 and that of diode 35,' each diode is partially delayed-by the other, the amount of delay increasing gradually from zero at approximately its own point of maximum response, corresponding `approximately to cutoff of the other diode. to a maximum or full cutoii' at the approximate point of maximum response of the other diode. This varying delay action is the cause for the progressively increasing slopesof the diode characteristics of Fig. 2 in the vicinity of the intermediate frequency of-the receiver. that is, the mean resonant frequency of the system, as the value of resistor l is progressively increased. However, this increase in slope does not become appreciable until the value of resistor I. is of the same order as, or greater than, that of resistors I1 and Il. -At the same time, it is noted that the'peaks of the diode characteristic fall progressively closer to the mean resonant frequency of the system, thus reducing the range of control. This is probably due primarily to the decreased loading of the tuned circuits of the selector. l v

In Fig. 3 there are shown characteristic dis- I criminator B curves for the circuit of Fig. 1 for values of resistor l0 varying from zero to 5 megohms, as indicated in the figure, the circuit having the following constants:

Tube li=type 6K7 Diodes 34 and II=type 6H6 Inductance "-882 microhenries Inductance I2-810 microhenries Mutual inductance. between inductances 3l and 32:4.4 microhenries (K=0.5%)

- Q of circuit I0, II=Q of circuit 32, II=50 Mean frequency of the system f=450 kilocyclcs Condenser ll= micro-microfarads Condenser 40=0.1 microfarad Resistors l1'and'l|=1 megohm each (3) the slope of the 8 curve away from the peakis more uniform and corresponds .more closely to that of ordinary control tube characteristics. thereby making the operation of the system. when utilized in an automatic-frequency control, more uniform when tuning toward and away. from a l signal.

In Fig. 4 there is shown another embodiment of the invention which is similar in operation to that of Fig. i and in which corresponding circuit elements have been given identical reference numerals. In the circuit of Fig. 4. the diodes 34 and Il have been replaced by trlode vacuum tubes 44 and 45.' The voltage across tuned circuit Il, ll is applied through a coupling lcondenser 43 to the cathode-grid circuits of tubes 44 and 4l with the same polarity while one-half the voltage across the circuit 32. 3l is also appliedto the control grid-cathode circuits of tubes u and u but with opposite poianty. 'one-half'- of the voltage across the circuit l2, il is yapplied to the anode-cathode circuitsof tubes 44 and 4I with-opposite polarity. A load circuit 'is provided for the system comprising series-connected resistors 41. 4l by-passed for alternating cur rents by condensers Bil, Il.

The operation of the. circuit of Fig. '4 is generally similar -to that of Fig. l. The vector sum and difference of the voltages of the primary and secondary tuned circuits o'f the system are applied respectively to the control grid-cathode circuits of tubes 44 and 4U. while the voltage of the secondary tuned circuit 32. 33 is applied to the anode-'cathode circuits.- A voltage is 'developed across resistor 48 by rectification in4 the gridcathode circuits of each of the rectiiiers 44 and 45, dependent upon the input signals thereto, and lis applied as a delay bias to the other of the rectiflers. thereby effecting an operation similar to that of the circuit of Fig. l. Thev bias vdeveloped across resistor 48 is double-peaked with respect to frequency.' When the receiver is of! tune the alternating yvoltage Vdeveloped between the cathode and gridof one of tubes 44 and 4l exceeds the bias across resistor 46. This allows the anode-cathode circuit oi" that vtriode to be conductive for a small fraction of the cycle. At this time the alternating voltage between the cathode and grid of the other tube is less than the bias developed across resistor 4G and the tube is out of! during the entire cycle. Vacuum tubes 44 and 45 also functionL as limiters in the circuit of Fig. 4, rendering the .output voltage derived from resistors 41, 48 more nearly constant for variations in the signal input to primary circuit ll, Il. I

#While the invention has been described with 4 reference to a frequency-responsive network utilized as the discriminator circuit of an automatic frequency control system, it will be understood that the frequency-responsive network of the invention' is not limited to this particular use but is applicable generally to frequency selective systems.

While there has lbeen described what is .at present considered to be the preferred embodiment of this invention, it will be obvious to those .I

skilled in the art that various changes and modifications may be made therein without departing r from the invention, and it is, therefore, aimed in the appended claims to cover all such changes.

and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

i. A high-sensitivity frequency-responsive network for operation over a limited frequency range comprising, an input circuit, means coupled to said input circuit for deriving va first voltage.

l means coupled to said input circuit for deriving a second voltage variablyeiyn phase with frequency over said range withiespect to said first voltage, two rectiners, means for applying to one of said rectifiers the sum andv to the other of said rectiiiers the difference of said two voltages, and means for developing a delay bias for each of said rectifiers from at least one of said sum and difference voltages, eachl of said biases being suiiicient, to reduce the output of the rectifier to which it is applied to zero at a frequency in the vicinity of the mean resonant frequency of said range, and means for deriving from said rectifier-s an output voltage varying in accordance'with the amplitudes and frequency of their corresponding applied voltages.

A'I6 ilas'mutualtosaid 2. A highssensitivity frequency-responsive network for operation overa limited frequency range comprising, an input circuit, means coupled to said input circuit for deriving a nrstvoltage.

second voltage variable in phase with frequency over said range with respect to saidiirst voltage. two rectifiers, means for applying to one of said rectifier-s the sum and to the other ofsaidrectiners the diiference of said two voltages. and means for developing a delay bias for each of said rectifier-s from at least one of said sum and difference voltages, one of said biases being suiiicient to reduce the output of the rectiner vto above the mean frequency of said range and the other of saidV biases being sumcient to reduce the output of the rectii'ier to which it is coupled to zero at a frequency slightly below -the mean frequency of said range, and means for deriving from said rectiners an output voltage varying in accordance with the amplitudes and frequency of v theirl corresponding applied voltages.

3. A high-sensitivity frequency-responsive network for operation over a limited frequency range comprising, van input circuit, means coupled to said input circuit for deriving a first voltage..

means coupled to said input circuit for deriving a second voltage variable in -phase with frequency over said range with respect to said iirst voltage, two rectiilers, means for applying to one of said rectiners the sum and to the other of said rectiiiers the difference of said two voltages. means for developing from each of said rectiiiersa delay bias for the other. each of said biases being sufficient to reduce the output of the rectiner to which it is applied to xero at a frequency in means coupled to said input circuit for deriving 'a which it is'applied to zero at a' frequency slightlybeing a maior portion of the output voltage of the rectifier from which it is derived, and means for deriving from said rectifiers a voltage varygreater than that of said common impedance.

the vicinity of the mean resonant frequency of Y Vsaid range. and means for deriving from said rectiers a voltage varying in accordance with the amplitudes and frequency of their corresponding applied voltages.

y 4. A high-sensitivity frequency-responsive network for operation over a limited frequency range comprising an input circuit. means'coupled to said input circuit for deriving a'iirst voltage. means coupled to said input circuit' for deriving avsecond voltage variable in phase with fre-V quency over said range with rewectto said rst ofsaid'rectifiers thesumandtotheotherof said rectiiiers the difference of said two voltages, means common to said twojrectiers for developing from each of said rectiiiers a bias mutual to said rectifiers, each of said biases being' sumcient to reduce the output of the rectifier to which it vis applied to aero at ajrequen'cy inthe vicinity of ,the mean resonant /frequency uof said range.-

and means for deriving from said rectiiiers a voltage varying in accorance with the amplitudes and frequenc'yoftheir corresponding com-V bined voltages.l r

work for operation overa-limited frequency range saidinputcircuit for deriving-a nrst means coupled tosaidinputcircuitfor deriving quencyoversaidramwithrcspccttosaidnrst 70 "time, WO recerl,

fromeachofsaidrectiiiersade rectiiiemeachofsaid comprising. all'inpiit\cir'c1rit.l means coupled tovoltage, two rectiners, meansffor applying to one Y means for applying the sum of said first and second voltages to one of said rectiilers, means for applying the difference of said first and second voltages to theother of said rectiilers, and means comprising said individual impedances for deriving an output voltage from said system.

7. A high-sensitivity frequency-responsive network for operation over a limited frequency range comprising, an input circuit, means coupled to said input circuit for deriving a nrst voltage, means coupled to said input. circuit forderiving a second voltage variable infphase with frequency over said range witlrrespect to said rst voltage, two rcctiiiers each comprising individual load circuits having a common load resistor and individual load resistors, the value of each of said individual load resistors being not appreciably greater than that of said common resistor, means for applying the sum of said nrst and second voltages to one of said rectiers. means for applying the differencel of said n rst and second voltages in the other said rectiiiers, and means comprising said indivi ual impedances for derivlng an output voltage from said system.

8. A high-sensitivity frequency-responsive network for operation over a limited frequency range comprising, an input circuit. means coupled to said input circuit forderiving a first voltage, means coupled to said input circuit for deriving ak second voltage variable'in phase with frequency over said range with-respect to said first voltage, two rectitlers comprising individual load circuits having a common load resistor and individual load resistors. the value oi Asaid common resistor being at least three `times that of'each of said individual load resistors. means for ap- Y. plying thesum of said iirst and second voltages put voltage from 'said system.v i

to' one of said rectiilers,meansfor applying the diiference-of said nrst andsecond voltages to the other of said rectiiiers.' and -means comprising said individual load resistors for deriving 'an out- 9. A high-sensitivity frequency-responsive network foroperation over a limited frequency range comprising, an input circuit. means coupledl to said input circuit for deriving a nrstvoltage,

twol inductively coupled resonant circuits Vfor deriving fromy said inputcircuit a second voltage variable in phase with quency over 'said range with rcspecttosaid'iirst voltage. two reotiflers each comprising individual load circuits having a commonimpedance and individual impedances. the value of each of said individua'lrimpedances being not appreciablv greater than vthat ofsald rnmonimpedance, means comprising a mid-tap on one of said two resonant'circuitsiorapplyingthesumofsaidl uil-standsecondvoitagcstooneofsaldrectifor deriving an output voltage from said system.

10. A high-sensitivity frequency-responsive network for operation over a limited frequency range comprising, an input circuit, means coupled to said input circuit `for deriving a first voltage, means coupled to said input circuit for deriving a second voltage-variable in phase with frequency over -said range with respect to said nrst voltage, two rectiiiers comprising individual load circuits having a common impedance and individual impedances, the value of each of said individual impedances being appreciably smaller than that of said common impedance, meansv for applying the sum of said first and second voltages to. one of said rectiilers, means for applying the difference of said first and second voltages to the other of said rectiners, and means comprising said individual impedances for deriving as anoutput vvoltage the algebraic sum of the voltages across said individual impedances,

1l. A high-sensitivity frequency-responsive network for operation over a limited frequency range comprising, an input circuit.' means coupled to said input circuit for deriving a iirst voltage.

means coupled to said input circuit for deriving a second voltage variable in phase with frequency over said range with respect to said first voltage, two vacuum-tube rectifiers each having input 'and output electrodes, means for applyingto the input electrodes of one of said rectiners the sum. and to the input electrodes of the other of said rectiilers the din'erence, of said rst and second voltages, means comprising a grid-bias resistor for said tubes common to the input circuits of said tubes for developing a delay bias from the input electrodes of each of said tubes and applying it to the input electrodes of the otherof said tubes, each of said biases being suflicient to reduce theoutput of the rectifier to which it is coupled to a low value in the vicinity of the mean resonant frequency of said rangefand means for deriving from said rectiiiers a voltage varying in accordance with the amplitudes and frequency of their applied voltage.

12. A high-sensitivity frequency-responsive network for operation over a limited frequency range comprising, an input circuit. means coupled in said input circuit'for deriving a first voltage, means coupled to saidinput circuit for deriving a second voltage variable in phase with frequency over said range with respect to said first voltage, two rectifiers, means for applying to one of said rectifiers the sum and to the other of said rectiiiers the difference of said first and one of said sum and difference voltages, each of 'said biases being sufficient to reduce the out-l put of the rectifier to which it is applied to a low value in the vicinity of the mean frequency of said range, said rectiners comprising means for limiting their outputs to relatively uniform values for a wide variation of the amplitude of the signal input to the system, and means for deriving from said rectiiiers a voltage varying in accordance with the amplitudes and frequency of their applied voltages.

13. A .frequency-responsive network for operation over a given frequency range comprising, means for developing from an' applied signal a first voltage which decreases with frequency in the vicinity o f the mean frequency of said range,

means for developing from said applied 'signal a second voltage which increases with frequency in thevicinity oi' the Ymean frequency of lsaid range, a pair of rectiiiers, means for individually applying each of said voltages to one of -said rectifiers,. means for applying a part of the output voltage of each `rectiiler as a delay bias on the other, each of said biases being sufficient to reduce the output of the rectifierfto which it is applied to zero at a frequency in the vicinity of the mean frequency, and means for in the vicinity of the mean frequency of saici range, a pair of rectiilers. means for individually applying'each of 'said voltages to one of said ,rectifiers, means for applying a part of the' output voltage of each rectifier as a' delay bias on the other. each of said biases being a major portion of the output voltage of the rectifier `from which it is derived, and means for deriv- 'ing from the output of each of said rectiiers an 15. A frequency-responsive network for operation over a. given frequency range comprising,

means for developing from an applied signal a first voltage which decreases with frequency in the vicinity of the mean frequency o f said range, means for developing from'said applied signal a second voltage which increases with frequency in the vicinity of the mean frequency of said range, a pair of rectifiers, means for individually applying each of said voltages to one of said rectliiers, means common to said two rectifers for developing from each of said rectiers a bias mutual to said rectiers, each of said biases being sufficient to reduce the output of the rectifier to A the frequency of the applied signal.

16. A frequency-responsive network for operation over a given frequency range comprising,

means for developing from an applied signal a first voltage which decreases with frequency in the vicinity of the mean frequency of said range, means for developing from said applied signal a second voltage which increases with frequency in the vicinity of .the mean frequency of said range, a pair of rectifiers. means for individually applying each of said voltages to one of said rectiers. individual load circuits for said rectiiiers having a common impedance and individual impedances, the value of each of said'individual impedances being not substantially greater' than said common impedance, and means for' deriving from the output of each of said rectiflers an effect which varies in accordance with the frequency of the applied signal. l'l. A frequency-responsive network for operation over a given frequency range comprising, means for developing from an applied signal a first voltage which decreases with frequency in the vicinity of the mean frequency of said range, means for developing from said applied signal a Y6Y I 91,091

Y second voltage which inceases with irequencyin the vicinity o! the mean frequency of ssid ranze,

n pair of rectiiiers.mean.s for individually applyinl each. oi' said voltases to one of said rectiers. individual load circuits for said rectitiers `having.eomxnoninxpodmnlsnlriixiciividudlimthe value of siiicl common impedance nom'r L. .I 

